Quack Quack Quack!
Why oh why does this keep coming up?
No. They are Silly. You would get faster if you did an extra half-an-hour's training instead of going to Sweatshop to buy one, or spent the money on Yoga classes for injury prevention, and you might not get faster but you would have more fun if you spent it on a night out.
They are ridiculous money-making junk.